Product families are the life cycle management consideration if the respective company decides to expand a single product offering. The product management team focuses on the life cycle management of the product which ensures that the product reaches its full potential as a particular product item or emerging product line in company's product mix. The product life cycle is a concept that attempts to describe product's unit sales post-launch through its eventual termination and also used to describe the possible development of an emerging market. The theory underlying the product life cycle is that unit sales will transition through four distinct product life cycle stages: introduction, growth, maturity and decline. The stages of the product life cycle, the time span of the entire life cycle and the shape of the life cycle will vary by product. External factors can impact the performance of a product, shortening or lengthening its life cycle and a company can influence a product's life cycle.